The present invention relates generally to apparatus and methods for removing occluding materials from body lumens. More particularly, the present invention relates to the construction and use of atherectomy catheters with an ability to view atheroma and other materials to be excised from blood vessels.
Cardiovascular disease frequently arises from the accumulation of atheromatous material on the inner walls of vascular lumens, particularly arterial lumens of the coronary and other vasculature, resulting in a condition known as atherosclerosis. Atherosclerosis occurs naturally as a result of aging, but may also be aggravated by factors such as diet, hypertension, heredity, vascular injury, and the like. Atheromatous and other vascular deposits restrict blood flow and can cause ischemia which, in acute cases, can result in myocardial infarction. Atheromatous deposits can have widely varying properties, with some deposits being relatively soft and others being fibrous and/or calcified. In the latter case, the deposits are frequently referred to as plaque.
Atherosclerosis can be treated in a variety of ways, including drugs, bypass surgery, and a variety of catheter-based approaches which rely on intravascular widening or removal of the atheromatous or other material occluding a blood vessel. Of particular interest to the present invention, a variety of methods for cutting or dislodging material and removing such material from the blood vessel have been proposed, generally being referred to as atherectomy procedures. Atherectomy catheters intended to excise material from the blood vessel lumen generally employ a rotatable and/or axially translatable cutting blade which can be advanced into or past the occlusive material in order to cut and separate such material from the blood vessel lumen. In particular, side-cutting atherectomy catheters generally employ a housing having an aperture on one side, a blade which is rotated or translated by the aperture, and a balloon or other deflecting structure to urge the aperture against the material to be removed.
Although atherectomy catheters have proven to be very successful in treating many types of atherosclerosis, existing catheter designs may be further improved to provide enhanced performance. For example, in nibbler-type atherectomy catheters and in material excising devices in general, it would be desirable to view the material to be removed prior to the removal step. Furthermore, it would be advantageous if this imaging capability were provided on the same catheter or device which performed the cutting procedure, thus reducing the amount of surgery time spent exchanging imaging and cutting devices. Although some existing catheters provide imaging capability, these devices generally require repositioning of the catheter and the cutting element between imaging and cutting procedures. This undesirably limits the ability of the surgeon to view the exact area of occlusive material to be removed prior to the cut. Such known devices also typically cause the user to first scan a large, less precise area of body lumen. It would be desirable if the device could image the precise area to be excised immediately preceding the cut. Additionally, the repositioning of the entire catheter between imaging and cutting may cause the cutting element to remove material from a location different than the one that was imaged. This decreases the effectiveness of the cutters and may accidentally damage the body lumen. Known imaging atherectomy catheters also have difficulty imaging through the area of the cutting window during catheter delivery. The sharp edges of the cutter on known atherectomy catheters are typically exposed during imaging and thus prevent simultaneous delivery and imaging by the device, since those exposed edges may accidentally catch and tear into the body lumen. For example, in U.S. Pat. No. 5,634,464, an imaging transducer is mounted on a rotatable cutter. Imaging can be performed either while the cutter is rotated or while it is merely axially translated (without rotation). In either case, the cutting blade is exposed during imaging.
For these reasons, it is desired to provide intravascular catheters which have imaging capability that enables a physician to differentiate between desirable tissue structure and undesirable fatty deposits to be removed from a body lumen. It is desirable that the imaging and cutting of material can occur without having to reposition the catheter between such procedures. It would also be desirable if the atherectomy catheter could interrogate and view the vessel while the cutter is delivered through the body lumen or vasculature. It would still further be desirable to provide atherectomy catheters having imaging capabilities which can be utilized while the blade of the atherectomy device is unexposed to the blood vessel. At least some of these objectives will be met by the catheter and method of the present invention described hereinafter and in the claims.